REACTIONS OF THE ETHYL RADICAL: VI. ADDITION TO CONJUGATED DIENES

1965 ◽  
Vol 43 (5) ◽  
pp. 1102-1109 ◽  
Author(s):  
A. C. R. Brown ◽  
D. G. L. James
Keyword(s):  
Rate Constants ◽  
Chain Transfer ◽  
Conjugated Dienes ◽  
Energy Of Activation ◽  
Conjugated Diene ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Ethyl Radical ◽  
Diene System ◽  
Rate Constants For Addition

Arrhenius parameters have been measured for the addition of the ethyl radical to the conjugated diene system in three representative molecular environments. Significant differences are found among the values of the energy of activation for addition, which are: 4.5 ± 0.2 kcal/mole for 2,3-dimethylbutadiene-1,3, 5.2 ± 0.3 kcal/mole for cyclohexadiene-1,3, and 6.6 ± 0.3 kcal/mole for 2,5-dimethylhexadiene-2,4. The increase in the energy of activation in this series is paralleled by an increase in the degree of shielding of the terminal carbon atoms of the conjugated system by substituent groups. The energy of activation for metathesis is significantly lower for cyclohexadiene-1,3 (5.4 ± 0.5 kcal/mole) than for 2,5-dimethylhexadiene-2,4 (7.6 ± 0.4 kcal/mole); the activated hydrogen atoms of the former are all secondary, whereas those of the latter are all primary. The ratio of the rate constants for addition and metathesis at 60° indicate that the radical homopolymerization of cyclohexadiene-1,3 and 2,5-dimethylhexadiene-2,4 should be subject to extensive degradative chain transfer.

Reactions of the ethyl radical I. Metathesis with unsaturated hydrocarbons

1958 ◽  
Vol 244 (1238) ◽  
pp. 289-296 ◽  
Keyword(s):  
Molecular Structure ◽  
Experimental Error ◽  
Frequency Factor ◽  
Energy Of Activation ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Common Value ◽  
Ethyl Radical ◽  
Molecular Reactivity ◽  
Bond Multiplicity

The kinetic study of the abstraction of the hydrogen atom from selected hydrocarbons by the ethyl radical reveals a natural correspondence between molecular structure and molecular reactivity. Values of the energy of activation of the series n -heptane, 1-heptene and 1-heptyne are distinct at 10·6 ± 0·4, 8·3 ± 0·5 and 7·6 ± 0·2 kcal mole -1 , respectively, and illustrate the activating influence of bond multiplicity. The group of olefines: 1-heptene, 1-octene, cyclo hexene and trans -4-octene appear to share a common value of 8·3 kcal mole -1 for the energy of activation, within the limits of experimental error. Values of the frequency factor correspond closely to the numbers of equivalent hydrogen atoms in the molecule of the hydrocarbons.

Shock-wave observations of rate constants for atomic hydrogen recombination from 2500 to 7000 °K: collisional stabilization by exchange of hydrogen atoms

1969 ◽  
Vol 310 (1501) ◽  
pp. 253-276 ◽  
Keyword(s):  
Shock Waves ◽  
Rate Constant ◽  
Rate Constants ◽  
Atomic Hydrogen ◽  
Functional Form ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Hydrogen Molecules ◽  
Hydrogen Recombination ◽  
Equilibrium Dissociation

Rate constants for the recombination of atomic hydrogen with hydrogen molecules, hydrogen atoms, and argon atoms as the third bodies are presented in functional form for the range of temperatures from about 2500 to 7000 °K and are critically compared with the results of other workers. The rate constants are evaluated from detailed analyses of spectrum-line reversal measurements of the fall in temperature accompanying dissociation behind shock waves in gas mixtures containing 20, 40, 50 and 60% of hydrogen in argon. The rate constants for recombination with hydrogen molecules ( k -1 ) and argon atoms ( k -3 ) fit the equations log 10 k -1 = 15.243 - 1.95 x 10 -4 T cm 6 mole -2 s -1 , log 10 k -3 = 15.787 - 2.75 x 10 -4 T cm 6 mole -2 s -1 , with a standard deviation of 0.193 in log 10 k -1 . The rate constant for recombination with hydrogen atoms is about ten times larger than these at 3000 °K and shows a steep inverse dependence on temperature ( ~ T -6 ) above 4000 °K. Below this temperature the power of this dependence decreases rapidly and there is strong evidence that the value of this rate constant has a maximum around 3000 °K. This behaviour is interpreted on the basis of a process of collisional stabilization by atom exchange, requiring an activation energy around 8 kcal mole -1 and taking place under conditions of vibrational adiabaticity. The over-all results indicate that the assumption of equality between the equilibrium constant and the ratio of the rate constants for dissociation and recombination is valid throughout the region of non-equilibrium dissociation and at all temperatures in the shock waves examined.

THE REACTIVITY OF THE CYCLIC POLYENES TOWARDS FREE RADICALS: III. ADDITION OF THE ETHYL RADICAL

1965 ◽  
Vol 43 (5) ◽  
pp. 1110-1119 ◽  
Author(s):  
A. C. R. Brown ◽  
D. G. L. James
Keyword(s):  
Molecular Structure ◽  
Free Radicals ◽  
Gas Phase ◽  
Energy Of Activation ◽  
Kcal Mole ◽  
Arrhenius Parameters ◽  
Ethyl Radical ◽  
Cyclic Polyenes

Arrhenius parameters have been measured for the addition of the ethyl radical to cycloheptatriene-1,3,5 and to bicyclo[2.2.1]heptadiene-2,5 in the gas phase; the values for the energy of activation are distinct at 6.4 ± 0.2 and 7.0 ± 0.1 kcal/mole respectively. The addition of the ethyl radical to benzene, cyclohexadiene-1,4, and cyclooctadiene-1,5 proceeds too slowly to be detected. The significance of these results is considered in conjunction with those obtained previously for cyclohexadiene-1,3 and cyclooctatetraene, and the possibility of interpreting the reactivity of the cyclic polyenes in terms of molecular structure is discussed.

Terpolymers of Ethylene, Propylene, and Tricyclo [5.2.1.0]Deca-2,5,8-Triene

1975 ◽  
Vol 48 (4) ◽  
pp. 747-764
Author(s):  
S. Cesca ◽  
S. Arrighetti ◽  
A. Priola ◽  
P. V. Duranti ◽  
M. Bruzzone
Keyword(s):  
Chain Transfer ◽  
Lewis Base ◽  
Side Reactions ◽  
Conjugated Diene ◽  
Ethylene Propylene ◽  
Diene System ◽  
Methyl Derivatives ◽  
Low Levels ◽  
Catalyst Systems ◽  
Acid Character

Abstract Tricyclo[5.2.1.0]deca-2,5,8-triene (1) or a mixture of its methyl derivatives was used as termonomer to obtain ethylene—propylene—triene terpolymers (EPTM) having unusual properties in the curing process, even at low levels of triene (ca. 1 wt %). Three types of catalyst systems have been investigated, based on VCl4, VO[O(CH2)3CH3]3, or V(acac)3 and (C2H5)2AlCl. Several parameters of the terpolymerization process were studied (e.g. Al/V mole ratio; catalyst and termonomer concentration; polymerization time; presence of a Lewis base or chain transfer agent) and their influence on Mv and EPTM composition were evaluated. Fractionation data and the use of model compounds allow to conclude that 1 enters EPTM chains randomly and by selective opening of the norbornenic double bond, whereas the conjugated diene system is involved in side reactions if the catalyst has some acid character or the concentration of the triene is above some critical value.

Kinetics and Mechanisms of the Acid-catalysed Hydrolysis of Tertiary Butyl Acetate

1962 ◽  
Vol 15 (3) ◽  
pp. 467 ◽  
Author(s):  
KR Adam ◽  
I Lauder ◽  
VR Stimson
Keyword(s):  
Rate Constants ◽  
Butyl Acetate ◽  
Arrhenius Equation ◽  
Aqueous Acetone ◽  
Energy Of Activation ◽  
Kcal Mole ◽  
Tertiary Butyl ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of the acid-catalysed hydrolysis of tertiary butyl acetate in water, in aqueous acetone, and in aqueous dioxan, over a range of temperature have been studied. The Arrhenius equation is not obeyed. In 40% water-60% acetone the energy of activation varies from 26-29 kcal mole-1 for temperatures 48-97 �C. This is due presumably to simultaneous hydrolyses via the AAL1 and the AAC2 mechanisms. By combination of oxygen-18 tracer results and kinetic results the rate constants for reactions by these mechanisms in water have been separated. The observed percentage of alkyl-oxygen fission in water varies from 85 at 25 �C to 97 at 60 �C. Rate constants for reactions by the AAL1 and the AAC2 mechanisms are expressed by the equations : k (sec-1 l mole-1) = 10l6.l exp (-27500/RT), and k (sec-1 l mole-1) = 107.9 exp (-l73OO/RT),respectively. However, the parameters of the latter equation may contain considerable errors because the extent of reaction by the AAC2 mechanism is small. In water and in 80% water-20% acetone, tertiary butyl acetate undergoes an uncatalysed solvolytic reaction, involving presumably the BAL1 mechanism. The variation of the rate of this reaction with temperature is expressed by the equation, k (sec-1) = 1012.3 exp (-26800/RT).

An electron spin resonance study of the reactions of hydrogen atoms with halocarbons

1986 ◽  
Vol 64 (11) ◽  
pp. 2192-2195 ◽  
Author(s):  
William E. Jones ◽  
Joseph L. Ma
Keyword(s):  
Rate Constants ◽  
Gas Flow ◽  
Esr Spectroscopy ◽  
Flow System ◽  
Electron Spin Resonance Study ◽  
Absolute Rate ◽  
Hydrogen Atoms ◽  
Vinyl Halides ◽  
Spin Resonance ◽  
Spin Resonance Study

The absolute rate constants for the reaction of H atoms with methyl- and vinyl-halides have been determined using esr spectroscopy and a conventional gas flow system. The rate constants determined at 298 ± 2 K at a pressure of 0.55 Torr are methane, (1.7 ± 0.3) × 10−17; ethane, (2.3 ± 0.5) × 10−17; methylfluoride, (4 ± 3) × 10−15; methylchloride, (8 ± 2) × 10−16; methylbromide, (2.1 ± 0.6) × 10−14; vinylfluoride, (1.47 ± 0.02) × 10−13; vinylchloride, (1.66 ± 0.08) × 10−13; and vinylbromide (4.07 ± 0.73) × 10−13 in units of cm3 molecule−1 s−1.

scholarly journals Tunnelling dominates the reactions of hydrogen atoms with unsaturated alcohols and aldehydes in the dense medium

2018 ◽  
Vol 617 ◽  
pp. A25 ◽  
Author(s):  
V. Zaverkin ◽  
T. Lamberts ◽  
M. N. Markmeyer ◽  
J. Kästner
Keyword(s):  
Functional Groups ◽  
Rate Constants ◽  
Aldehyde Group ◽  
Dense Medium ◽  
Hydrogen Atoms ◽  
Hydrogen Addition ◽  
Reaction Rate Constants ◽  
Quantum Chemical Methods ◽  
Experimental Findings ◽  
Recombination Reactions

Hydrogen addition and abstraction reactions play an important role as surface reactions in the buildup of complex organic molecules in the dense interstellar medium. Addition reactions allow unsaturated bonds to be fully hydrogenated, while abstraction reactions recreate radicals that may undergo radical–radical recombination reactions. Previous experimental work has indicated that double and triple C–C bonds are easily hydrogenated, but aldehyde –C=O bonds are not. Here, we investigate a total of 29 reactions of the hydrogen atom with propynal, propargyl alcohol, propenal, allyl alcohol, and propanal by means of quantum chemical methods to quantify the reaction rate constants involved. First of all, our results are in good agreement with and can explain the observed experimental findings. The hydrogen addition to the aldehyde group, either on the C or O side, is indeed slow for all molecules considered. Abstraction of the H atom from the aldehyde group, on the other hand, is among the faster reactions. Furthermore, hydrogen addition to C–C double bonds is generally faster than to triple bonds. In both cases, addition on the terminal carbon atom that is not connected to other functional groups is easiest. Finally, we wish to stress that it is not possible to predict rate constants based solely on the type of reaction: the specific functional groups attached to a backbone play a crucial role and can lead to a spread of several orders of magnitude in the rate constant.

Rate constants for reaction of hydrogen atoms in aqueous solutions

1971 ◽  
Vol 75 (4) ◽  
pp. 449-454 ◽  
Author(s):  
Robert H. Schuler ◽  
Pedatsur Neta ◽  
G. R. Holdren
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Hydrogen Atoms

The photochemical and thermal decompositions of hydrogen sulphide

1953 ◽  
Vol 216 (1126) ◽  
pp. 344-361 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Quantum Yield ◽  
Hydrogen Sulphide ◽  
Low Temperatures ◽  
Room Temperature ◽  
Large Fraction ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Photochemical Decomposition ◽  
Bimolecular Mechanism

The photochemical decomposition of hydrogen sulphide has been investigated at pressures between 8 and 550 mm of mercury and at temperatures between 27 and 650° C, using the narrow cadmium line ( λ 2288) and the broad mercury band (about λ 2550). At room temperature the quantum yield increases with pressure from 1.09 at 30 mm to 1.26 at 200 mm. Above 200 mm pressure there was no further increase in the quantum yield. Temperature had little effect on the quantum yield at λ 2550, but there was a marked increase in the rate of hydrogen production between 500 and 650° C with 2288 Å radiation. This may have been caused by the decomposition of excited hydrosulphide radicals. The results are consistent with a mechanism involving hydrogen atoms and hydrosulphide radicals. The mercury-photosensitized reaction is less efficient than the photochemical decomposition, the quantum yield being only about 0.45. The efficiency increased with temperature and approached unity at high temperatures and pressures. This agrees with the suggestion that a large fraction of the quenching collisions lead to the formation of Hg ( 3 P 0 ) atoms. The thermal decomposition is heterogeneous at low temperatures and becomes homogeneous and of the second order at 650° C. The experimental evidence suggests the bimolecular mechanism 2H 2 S → 2H 2 + S 2 . The activation energies are 25 kcal/mole (heterogeneous) and 50 kcal/mole (homogeneous).

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